Elastic fluid apparatus



ELASTIC FLUID APPARATUS Fig.2.

Sept. 27, 1966 J. M. ALLEN ET AL ELASTIC FLUID APPARATUS 5 Sheets-Sheet 5 Filed Nov. 14, 1963 United States Patent vauia Filed Nov. 14, 1963, S91. No. 323,737 8 Claims. (CI. 25.3-39.1)

This invention relates to axial-flow elastic fluid utilizing machines such as turbines and compressors, more particularly to blading employed therein, and has for an object to provide improved blading structure of this type.

In axial-flow elastic fluid utilizing machines, especially turbines, the vane portions of the diaphragm blades are highly susceptible to cracking at their trailing edges, due to transient thermal stresses which arise during starting and shutdown of the machine. These stresses are often high enough to cause the blade material to exceed the yield point, thereby leaving residual stresses in the blades after the blades attain steady state temperature. These stresses can remain for long periods of time, depending on the stress relaxation properties of the blade material, and, therefore, in combination with thermal stress cycling (caused by operational starting and shutdown) can lead to blade failure in a short period of time.

In view of the above, it is another object of the invention to provide a bladed diaphragm in which the thermal stresses are substantially minimized.

Another object is to provide an improved cooled structure for an axial-flow elastic fluid utilizing machine in which rotating blade excitation resulting from coolant leakage at descrete circumferential locations is avoided.

Yet another object is to provide a bladed diaphragm structure for a machine of the above type, which structure has improved vibration damping characteristics.

Although the invention is primarily intended for axialflow gas turbines, it may be advantageously employed in axial-flow elastic fluid compressors and turbines motivated by any suitable hot elastic fluid.

Briefly, in accordance with the invention there is provided a diaphragm structure disposed within a tubular casing and having an annular array of individual stationary blades disposed in cooperative relation with an annular row of rotatable blades. The stationary blades are held at their radially outermost tips by a shroud ring and at their base portions by a flexible band. The bases are of boxlike structure with mutually interengaging marginal portions and the interengaging portions are maintained in slidable abutment with each other by the band. The band is of such flexibility that it permits the blades to bend in circumferential and axial directions and to expand individually in radial direction without imposing thermal stresses therein and is further effective to induce damping of the blades by maintaining the sliding abutment of the bases.

The bases are of hollow form defining individual plenum chambers with fluid outlet aperatures and the vanes are provided with passages for conducting coolant fluid such as air, to the plenum chambers in the bases. Also, an annular structure is provided in encompassing relation with the shroud ring and jointly therewith defining an annular plenum chamber.

In operation, coolant fluid is directed to the annular plenum chamber, thereby primarily encompassing the diaphragm structure with the coolant and minimizing heat transfer to the casing by radiation. The coolant is then directed through the stationary blades with concomitant cooling of the stationary blades, and finally expelled through the outlets in the bases to cool the highly stressed rotor periphery and the root portions of the rotatable blades.

The above and other objects are effected by the invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

FIGURE 1 is a longitudinal sectional view of a portion of an axial-flow gas turbine incorporating the invention;

FIGURE 2 is a transverse sectional view taken on line IIII of FIGURE 1, with-some portions cut away for clarity;

FIGURE 3 is a perspective view of one of the stationary blades illustrated in FIGURES 1 and 2; and

FIGURE 4 is a view similar to FIGURE 2, but showing another embodiment.

Referring to the drawings in detail, in FIGURES 1 and 2 there is shown a portion of an axial-flow gas turbine 10 having the invention incorporated therein. Only those portions concerned with the invention are shown, since gas turbines of this type are well known. Briefly, gas turbines of the type illustrated employ tubular shell or casing structure 12 having annular diaphragm or nozzle structures 14 and 14a disposed therein and cooperatively associated with a rotor structure 16. Each of the diaphragm structures is provided with an annular row of stationary blades 17 and 17a in juxtaposed relation with corresponding annular rows of rotatable blades 18 and 18a, respectively, carried by the rotor structure 16.

Hot pressurized products of combustion, generated in suitable fuel combustion structure (not shown), are directed in an annular stream in the direction indicated by the arrow G (FIGURE 1) past the two expansion stages formed by the blades 17 and 18, and the blades 17a and 18a, thereby rotating the rotor structure 16 to provide useful mechanical power, as well known in the art. Although only two expansion stages have been illustrated, more or less may be employed, as desired.

In accordance with the invention, the stationary blades 17 are provided with radially outermost tips 20, vane portions 21 and radially innermost base portions 22. For reasons well known in the art, the vane portions are air foil shaped with rounded leading edges L and thin trailing edges T (see FIGURES 1 and 3). The blades '17 are of hollow construction and formed in a manner to provide a fluid flow passageway 23 extending through the vane portion 21 and communicating with a space or plenum chamber 24 formed in the base 22. The base 22 is of substantially box-like shape with forwardly and rearwardly facing wall portions 25 and 26 as Well as opposed wall portions 27 and 28 connected to the forward and rearward wall portions 25 and 26, a radially inner wall portion 29, and a platform 30 completing the enclosure for the plenum chamber 24. The rearwardly facing wall 2 6 is provided with a plurality of fluid outlet apertures 31 of predetermined size and fluid flow characterrstics.

The blades 17 are attached at their outermost tips 20 to a frustoconical shroud ring 32 having a plurality of apertures 33 disposed in registry with the passages 23 in the blades. On the other hand, the blades are maintained at their innermost ends in abutment with each other by channel-shaped flange portions 34- extending from the side walls 27 and 28, respectively, of the bases 22. Accordingly, in the annular array of blades 17, the flange portions 34 of each blade are disposed in engaging and interlocking relation with the wall portion 28 of its neighboring blade. Hence, the stationary blades 17 are maintained in the proper position for operation but are still individually free to expand in radially inwardly direction during the operation as well as to bend laterally in the circumferential direction, indicated by the arrow B. The innermost walls 29 of the bases are provided with bosses 37 having shoulders 38, and an annular band 39 is rigidly attached to the bosses 37. In the illustration the 'strip material, which as best shown in FIG. 1 is preferably of rectangular shape with its wide dimension disposed in parallel relationship with the wall 29 and its narrow dimension disposed in parallel relation with the longitudinal axis of the blades (see FIGURE 1). The band 39 is further formed of material having sufficient flexibility to permit the blades 17 to expand relative to each other without imparting internal stresses in the blades, yet of suflicient rigidity and strength to maintain the bases 'of the blades in properly assembled relationship.

There is further provided a pair of spacer disc members 42 and 43 for maintaining the diaphragm structure 14 in internally and concentrically spaced relation with the outer casing '12. The spacer discs 42 and 43 may be suitably secured to the casing structure 12 at their outermost circumferential peripheries and to the shroud ring '32 at their radially innermost circumferential peripheries, for example by rabbeted interlocking portions 44, as illustrated in FIGURE 1.

The flow passage for the motive fluid G is provided by suitable stationary tubular fairing structure 45 and 46. Also, a frustoconical ring member 47 is provided in encompassing relation with the rotor. blades 18 and maintained in concentrically spaced relation with the outer casing 12 by the spacer member 43 and a spacer member 49. Since the flow path for the motive fluid G is divergent in downstream direction with respect to motive fluid flow as well known in the art, the spacers 42, 43 and 49 are formed to maintain the shroud ring 32 and the ring 47 in the position shown in FIGURE 1 to permit such a diverging flow path to be maintained.

A ring member 51 of channel-shaped cross section, formed of suitable sheet material, is disposed in encompassing fiuid-tight relation with the shroud ring 32 and forms an annuar plenum chamber 52 providing a common flow communication for all of the apertures 33 in the shroud ring and the passageways 23 in the blades. This channel member 51 and shroud ring 32, in this embodiment, are of unitary construction so that the entire diaphragm structure 14 forms a complete and integrated circular assembly.

Coolant fluid, such as air or the like, is directed to the plenum chamber 52 by a plurality of tubes or con- 'duits 53 extending radially through the outer casing 12 and connected thereto in leakproof relation by suitable bellows 54, so that in operation the bellows permit the shell structure and/or the tubes to freely expand and contract relative to each other without impairing the seal 55 at the casing 12.

The fluid may be directed from any suit-able pressurized fluid supply (not shown), as indicated by the arrow 56 in FIGURE 2, and thence directed to each of the fluid conduits 53 by suitable manifold structure indicated by the dot-dash lines 57 in FIGURES 1 and 2.

' The rotor structure 16 may be formed in any suitable inanner, however, in the illustration it is of the aggregative type and includes rotor discs 58 and 59 for supporting the rotatable blades 18 and 18a, respectively. The disc 58 is provided with complementary oppositely extending annular flange portions 60 and 61 and, in a similar manner, the rotor discs 59 is provided with complementary flanges 6'1 and 60. The rotor structure 16 further includes an end closure member 64 and the aggregate is maintained in assembled relation by a plurality of through bolts 65 for clamping the closure member 64, the discs 58 and 59 (and subsequent discs, not shown) together. The blades 18 and 18a may be of substantially identical type and are provided with root portions 66 of the well known fir tree or serrated type received in complementary recesses 67 formed in the rotor discs 58 and 59.

In operation, as hot motive fluid is directed past the stationary blades 17 and the rotatable blades 18 by the motive fluid stream G, the diaphragm structure 14 rapidly becomes heated and undergoes some relative thermal expansion. This thermal expansion is initially not usually uniform in the blades. However blade expansion is permitted to occur freely in radially inward direction, since the blades 17 are rigidly fastened to the shroud ring 32 but only slidably connected to each other by abutment at the bases 22. Hence, minimal internal thermal stressing occurs. Furthermore, should one or several of the blades 17 undergo somewhat greater transient expansion or bending than adjacent stationary blades 17, the band 39 permits the elongation and bending of one or more of the blades to occur with minimum interaction between blades.

In addition to the above, blading is often subject to vibrational effects by the gas flow past the blades. Such vibration is often harmful to the blades and may cause damage thereto. Should the blades 17 begin to vibrate, eflective vibration damping is attained by the friction of the slidable abutment between the adjacent bases 22 at the area of interlocking engagement between the complementary locking flanges and Walls 28. The vibration damping characteristics of the blades are further enhanced by the band 39, since it maintains the bases 22 in frictionally slidable abutment with each other during all phases of operation. During operation, the band 39 may flex circumferentially as required to permit the elongation of the blades to occur as mentioned above.

Also, during operation, coolant fluid is directed through the manifold structure 57 and the conduits 53 to the annular plenum chamber 52 and, thence, through the blade passages 23 into the plenum chambers 24 in the bases 22. From the chambers 24, the fluid is ejected through the fluid outlet apertures 31 in discrete jets towards the root portions 66 of the adjacent rotatable blades 18. Accordingly, the entire diaphragm structure 14 is prevented from becoming excessively overheated by the continuous flow of the fluid therethrough. In addition thereto, the fluid flow through the apertures 31 attains a substantially high velocity and impinges upon the rotatable blade roots 66 and the peripheral portion of the rotor disc 58 to minimize overheating of these highly stressed rotor portions, it being understood that, during operation, the rotatable blades 18 are subjected to high centrifugal and tangential forces especially in their root portions 66, and the rotor disc 58 is also subjected to such stresses in its periphery due to the transmission of the forces from the blades 18 by the roots 66.

In addition to the above, the channel ring structure 51 serves to restrict the transmission of heat from the motive fluid G to the outer casing structure 12, since most of such transmitted heat is usually effected by radiation. This reduction in heating effect of the outer casing structure 12 by the motive fluid is enhanced by the circular layer of coolant fluid maintained in the annular plenum chamber 52 during operation. Furthermore, during operation, since the plenum chamber 52 is fully enclosed'by the channel ring 51 and the shroud ring 32, leakageof coolant fluid past the shroud ring 32 into the motive fluid stream G is obviated, thereby avoiding excitation of the rotatable blades 18, which could otherwise induce harmful vibration therein.

The diaphragm structure 14a is substantially the same as the diaphragm structure 14 already described. However, since the diaphragm structure 14:: is interposed between the rotatable blades 18 disposed upstream thereof and the rotatable blades 18a disposed downstream thereof, it may if desired be slightly modified to include a plurality of outlet apertures 31a for expelling the fluid from the plenum chambers 24 in upstream direction toward the downstream face of the blade roots 66. With this arrangement, the rotatable blade roots 66 and the rotor disc 58 are provided with cooling on both faces.

After the air is ejected through the apertures 31. and

31a it is directed into the motive fluid flow passageway and is directed downstream therewith.

FIGURE 4 illustrates a modification of the structure shown in FIGURES 1 and 2. Since this embodiment is similar to the embodiment shown in FIGURES 1 and 2, and operates in substantially the same manner, the rotor structure has not been shown and only those portions that are modified will be described. In this embodiment, there is provided a tubular casing structure 112, similar to the casing 12 but divided in a horizontal plane into upper and lower half portions 112a and 112b, respectively, and provided with axially extending flanges 113 joined together by suitable bolts.

Within the casing 112 there is provided an annular diaphragm structure 114 similar to the diaphragm structure 14 but divided into upper and lower half portions 114a and 11%. The upper diaphragm half portion 114a is disposed in the upper casing half portion 112a, while the lower diaphragm half portion 11417 is disposed in the lower casing portion 11217.

The nozzle blades 117 are disposed in an annular row and formed in the same manner as the blades 17. However, the blades in the upper diaphragm half 114a are held at their outer tips by a semi-circular shroud ring 132a and at their bases 122 by a semi-circular band 139a. Similarly, the blades in the lower diaphragm half 11412 are held at their outer tips by a semi-circular shroud ring 13212 and at their bases 122 by a semi-circular flexible band 13%.

Upper and lower semi-circular plenum chambers 152a and 152b are formed by upper and lower semi-circular channel members 151a and 151b, disposed in encompassing leakproof relation with the shroud ring halves 132a and 132b, respectively. Adjacent their juxtaposed end portions (only one pair of end portions shown) the shroud channel members 151a and 151b are provided with end walls 133a and 133b, respectively, extending into sealing abutment with their associated shroud ring halves 132a and 132b.

With the above arrangement, assembly is readily accomplished by placing the lower diaphragm half 114b in the lower casing half 112b, placing the upper diaphragm half 114a in the upper casing half 112a, then placing the upper casing half 112a upon the lower casing half 112k and bolting the two casing halves together at the flanges 113. Disassembly for repair or replacement of the diaphragm structure 114 is readily accomplished by reversing the above steps.

Even though the diaphragm halves 114a and 11417 are closely fitted to each other at their juxtaposed ends, a space 134 difficult to eliminate. Further, during operation, with attendant thermal expansion of the components, the width of the space 134 may increase. However, since the plenum chambers 152a and 15211 are rendered separate and distinct from each other by the end walls 133a and 133b, leakage of coolant fluid from the plenum chambers 152a and 15211 past the space 134 into the motive fluid path G is substantially obviated, with attendant minimization of excitation of the rotor blades.

It will now be seen that the invention provides an arrangement that is highly improved and is effective to minimize internal stressing of the nozzle blades by thermal effects and is further effective to provide highly effective vibration damping characteristics. In addition, the arrangement further provides a reduction in the heating effect of the outer casing structure by radiation of heat from the motive fluid and eliminates coolant leakage excitation of rotating blades.

It will further be seen that with the arrangement described, the coolant fluid serves the additional purpose of preventing overheating of the rotatable blade roots and the periphery of the rotor disc structure.

Although several embodiments of the invention have been shown and described, it will be obvious to those 6 skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

We claim as our invention: 1. A bladed diaphragm structure for an axial flow elastic fluid utilizing machine, comprising an annular row of radially extending blades, said blades having a vane portion, a radially outermost tip portion and a radially innermost base portion, an annular shroud structure cooperatively associated with said tip portions for supporting said blades, said base portions being similarly shaped and having complementary interlocking portions, and an annular band in the form of a relatively thin strip rigidly connected to each of said base portions and maintaining said base portions in frictionally interlocking relation with each other, said band being of sufficient flexibility to permit radial expansion and bending of said blades in circumferential direction and to effect vibrational damping of said blades. 2. The structure recited in claim 1 in which said base portions are provided with radially innermost wall portions jointly defining a circular surface, and means are provided on each of said innermost wall portions for rigidly connecting said base portions to said band. 3. The structure recited in claim 1 in which said base portions are provided with arcuate radially innermost wall portions jointly defining a substantially cylindrical first surface, means are provided on each of said innermost wall portions for connecting said base portions to said band, and said band has a radially outermost substantially cylindrical surface in concentric relation with said first surface. 4. The structure recited in claim 1 in which said base portions are of hollow box-like form and define plenum chambers, said blades are provided with passages communicating with and efiective to conduct a coolant fluid to said plenum chambers, and said base portions are provided with outlet apertures for expelling the coolant fluid. 5. A bladed diaphragm structure for an axial flow elastic fluid utilizing machine, comprising an annular row of radially extending blades, said blades having a vane portion, a radially outermost tip portion and a radially innermost base portion, an annular shroud structure cooperatively associated with said tip portions for supporting said blades, said base portions being of arcuate shape and having abutting juxtaposed end portions, disposed in an annular array, and an annular band structure of thin rectangular crosssection encompassed by and rigidly connected to each of said base portions and maintaining said base portions in radially slidable abutment with each other, said band being of sufficient radial flexibility to permit radial expansion of said blades and bending of said blades in circumferential direction, and to effect vibrational damping of said blades. 6. An axial flow elastic fluid utilizing machine comprising a tubular casing, a rotor disposed within said casing and having an annular row of rotatable blades, said blades having root portions afiixed to said rotor, a diaphragm structure disposed within said casing and having an annular row of stationary blades in cooperative relation with said rotatable blades, said stationary blades having a vane portion, a radially outermost tip portion and a radially innermost base portion,

an annular shroud structure cooperatively associated with said tip portions and supporting said stationary blades,

said base portions being similarly shaped and having complementary engaging portions,

said base portions being hollow and said vane portions having passages communicating with said base portions,

means for directing a coolant fluid through said passages to said base portions,

said base portions being further provided with fluid outlets for directing the coolant fluid against the root portions of said rotatable blades, and

an annular band structure rigidly connected to each of said base portions and maintaining said base portions in engaging relation with each other, said band being of suflicient flexibility to permit radial and circumferential expansion of said stationary blades yet etfect vibrational damping of said stationary blades.

7. The structure recited in claim 6 and further including means for supporting the diaphragm structure inconcentric spaced relation with the casing and jointly with the latter forming an annular space, and

means encompassing the shroud and jointly therewith defining an annular plenum chamber providing a common coolant fluid communication with the passages in the vane portions,

said shroud encompassing means being further effective to impede heat exchange between the diaphragm and the casing by radiation.

8. An axial flow elastic fluid utilizing machine comprising a tubular casing divided into halves of semicircular cross-section;

a rotor disposed in said casing and having an annular row of rotatable blades,

' said blades having root portions aflixed to said rotor;

an annular diaphragm structure disposed within said casing and having an annular row of stationary blades in cooperative relation with said rotatable blades,

said stationary blades having a vane portion, a radially outermost tip portion and a radially innermost base portion;

said diaphragm being divided into semicircular halves,

each of said diaphragm structures having means coop- 1 eratively associated with said blade tip portions and defining a fluid tight outer semicircular plenum chamber, i

said stationary blades having passages communicating with said plenum chamber; and

means for directing coolant fluid to said plenum chamber;

said base portions being similarly shaped and having complementary engaging portions, and

each of said diaphragm halves being provided with a flexible band rigidly connected to each of said base portions and maintaining'said base portions in engaging relation with each other.

References Cited by the Examiner UNITED STATES PATENTS 2,530,908 11/1950 Ray 25378 FOREIGN. PATENTS 980,869 1/1951 France 1,340,752 9/1963 France.

787,666 12/1957 Great Britain.

MARTIN P. SCHWADRON, Primary Examiner.

SAMUEL LEVINE, Examiner. E. POWELL, Assistant Examiner. 

1. A BLADED DIAPHRAGM STRUCTURE FOR AN AXIAL FLOW ELASTIC FLUID UTILIZING MACHINE, COMPRISING AN ANNULAR ROW OF RADIALLY EXTENDING BLADES, SAID BLADES HAVING A VANE PORTION, A RADIALLY OUTERMOST TIP PORTION AND A RADIALLY INNERMOST BASE PORTION, AN ANNULAR SHROUD STRUCTURE COOPERATIVELY ASSOCIATED WITH SAID PORTIONS FOR SUPPORTING SAID BLADES, SAID BASE PORTIONS BEING SIMILARLY SHAPED AND HAVING COMPLEMENTARY INTERLOCKING PORTIONS, AND AN ANNULAR BAND IN THE FORM OF A RELATIVELY THIN STRIP RIGIDLY CONNECTED TO EACH OF SAID BASE PORTIONS AND MAINTAINING SAID BASE PORTIONS IN FRICTIONALLY INTERLOCKING RELATION WITH EACH OTHER, SAID BAND BEING OF SUFFICIENT FLEXIBILITY TO PERMIT RADIAL EXPANSION AN D BENDING OF SAID BLADES IN CIRCUMFERENTIAL DIRECTION AND TO EFFECT VIBRATION DAMPING OF SAID BLADES. 